How the size of our brain means we all see the world around us in a different way

The way we view the world depends on the size of one small part of our brain, according to a new study,

The primary visual cortex - the area at the back responsible for processing what we view around us - is known to vary in size by up to three times from one individual to the next.

This affects the way we see the world, meaning we all see the world differently researchers say.

An MRI scan showing the visual cortex in yellow at the back of the brain. The size of this influences how we view our environment

Dr Samuel Schwarzkopf, of University College London, said: 'Our work is the first to show that the size of part of a person's brain can predict how they perceive their visual environment.'

The team showed a
series of optical illusions to thirty healthy volunteers.

These included
the Ebbinghaus illusion, a well-known illusion in which two circles of
the same size are each surrounded by circular 'petals'; one of the
circles is surrounded by larger petals, the other by smaller petals.

Most people will see the first circle as smaller than the second one

In a second experiment called the 'Ponzo' illusion the volunteers were shown two identically sized circles superimposed onto the image of a tunnel where the circle placed further back appears larger than that placed near the front.

By adapting these illusions, the researchers were able to show that individual volunteers saw the illusions differently.

The Ebbinghaus illusion: Most people will see the first circle as smaller than the second one even though they are both the same size.

For example, some people saw a big, although illusory, difference in size between the two circles, but others barely saw any difference in apparent size.

Using brain scans the researchers were also able to measure the surface area of the primary visual cortex in each volunteer and found a great deal of variability in the size of this area.

Surprisingly, there was a strong link between its size and the extent to which volunteers perceived the size illusion - the smaller the area, the more pronounced the visual illusion.

Dr Schwarzkopf, whose findings are published in Nature Neuroscience, said: 'Optical illusions mystify and inspire our imagination, but in truth they show us that how we see the world is not necessarily physically accurate, but rather depends a lot on our brains.

'Illusions such as the ones we used influence how big something looks; that is, they can trick us into believing that two identical objects have different sizes.

'We have shown that precisely how big something appears to you depends on the size of a brain area that is necessary for vision. How much your brain tricks you depends on how much 'real estate' your brain has put aside for visual processing.'

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How the size of our brain means we all view the world in a different way